Modern telephony services deployed in the Public Switched Telephone Network (PSTN) commonly rely on distributed transaction oriented telephony functionality, such as, for example Intelligent Network and/or Advanced Intelligent Network (IN/AIN) functionality in order to deliver sophisticated call control services to subscribers. Typically, this distributed functionality involves various network elements (e.g. Service Control Points (SCP's), Intelligent Peripherals (IPe's) and Interactive Voice Response (IVR) servers) and transaction-based protocols (such as Intelligent Network Application Part (INAP), and Transaction Capability-Application Part (TCAP)) deployed in the Common Channel Signaling (CCS) network. INAP and TCAP operate over conventional Signaling System 7 (SS7) infrastructure, and supplements legacy Integrated Services Digital Network-User Part (ISUP) signaling by providing a query/response protocol for accessing routing information and telephony services provided by IN/AIN capable network elements within the CCS network.
A deficiency of the current PSTN/CCS network is that its monolithic architecture and slow (64 kbs) signaling speed reduces network scalability. As the amount of telephony traffic increases, network service providers have increasing difficulty provisioning sufficient CCS network resources to handle the associated ISUP and INAP/TCAP signaling. In this respect, one particular difficulty is the need to provide each network element (e.g. an SCP) with sufficient SS7 signaling ports. Typically, the number of SS7 signaling ports is limited by both the hardware and software of the network element implementation. In the case of legacy CCS network elements, the monolithic design of both the hardware and software tends to make the addition of new SS7 signaling ports difficult, and therefore expensive. However, failure to provision sufficient SS7 signaling ports can lead to port exhaustion, and consequent reduction in services as the affected network element is unable to accept any new ISUP or TCAP messages until a port becomes available.
Another limitation of the legacy CCS network is that its monolithic design, and the high cost of CCS network elements, create significant barriers to the entry of network service providers who lack CCS network infrastructure.
In order to address issues of scalability within the PSTN, various efforts have been made to deploy telephony services in a broadband packet network such as an internet protocol (IP) network. Various protocols have been proposed to enable this functionality, including various Voice over IP (VoIP) protocols for carrying bearer traffic, as well as session set-up and routing protocols (such as Multi-protocol Label Switched Path (MPLS) and Session Initiation Protocol (SIP)) for establishing communications sessions and for routing the bearer traffic through the network. In general, it is also possible to deploy resources in a broadband packet network that enable services similar to those provided by the legacy CCS network. However, in order to establish telephone connections between points in the PSTN and a packet network, interaction between resources of the broadband packet and CCS networks is essential. One method of accomplishing this has been proposed by V. Gurbani in an Internet Engineering Task Force (IETF) draft entitled “Accessing IN services from SIP networks”. FIG. 1 is a block diagram illustrating the system of Gurbani for enabling IN/AIN functionality for telephony services deployed in a SIP network 2. As shown in FIG. 1, Gurbani teaches an IN state machine 4 overplayed on the conventional SIP state machine 6 within a SIP server 8 of the SIP network 2. The IN state machine 4 operates to generate conventional TCAP messages reflecting the state of the SIP state machine 6, and forwards these messages though the legacy CCS network 10 to an IN/AIN capable device 12 (e.g. an SCP and/or an IPe). TCAP messages (e.g. response messages) are received over the CCS network 10 by the IN state machine 4 and passed to the SIP state machine 6 to control call setup through the SIP network 2.
Thus, in the system of Gurbani, the IN state machine 4 operates as an interface between the SIP network 2 and the conventional CCS network 10, which enables a SIP server 8 to emulate a Service Switch Point (SSP) of the PSTN for the purposes of accessing IN/AIN functionality. However, this system suffers from the limitation that it increases the amount of TCAP traffic in the CCS network 10, and thus increases the risk of signaling port exhaustion in the CCS network element 12. This risk increases as the amount of telephony traffic in the SIP network 2 increases.
Accordingly, a method and apparatus that enables access to distributed transaction oriented telephony functionality for telephony services deployed in a broadband packet network while mitigating the risk of signaling port exhaustion in CCS network elements, remains highly desirable.